Your body is pretty amazing. At any given point you have many biological processes going on -- circulatory, digestive, brain & central nervous systems and more. Learn about these body systems as well as the eye, ears, nose and throat.

Fat cells develop steadily from birth to the early twenties. Research shows that it's only the size of the cells in individuals that differs. Learn more about fat and metabolism in "Extreme Bodies" on Discovery Channel.

Think it's a hassle when your car breaks down? Try finding a spare organ when your body gives out. Thanks to years of research, scientists are now amassing a "body shop"Ã‚Â of sorts, dealing not in tires or mufflers, but in bladders, bones and breasts.